I have been a buyer and I have been a seller, and I once taught a course called the Science of Selling. It was all about the fight/flight mechanism and how it affects sales. So, while I'm not exactly the king of sales I can tell you with absolute certainty how to muck up a sale.

1. You can't sell something that people don't use.

I contribute articles, such as and including this one, to Entrepreneur. That doesn't attract groupies or advances from publishers clamoring for me to write the next great American novel, but it brings a lot of sales pitches for things I don't use.I get sales pitches from Chinese companies that make injection molded parts. They don't say parts for what, but I am not going far out on a limb to presume it's not part of anything I will be assembling in my garage.

To pitches such as that I usually fire back a nasty missive on the need for qualifying leads using words that decorum doesn't allow me to print here. Before attempting to sell something to somebody, ask them some questions:

1. What does your company do?

2. What do you do at the company?

3. Does your company ever buy your goods or service?

The person is not a prospect unless their answers mesh with what you are selling. Tell them what you sell and ask if they know anyone who needs what you're selling. If, by some weird cosmic alignment, you sell someone something they don't need, you will never make a second sale to them.

2. Sales is about connecting a need to a solution.

To paraphrase the familiar adage, when you sell hammers, you see every problem as a nail. The temptation is strong to twist our view of the customer's need until it fits the solution we're selling. Connecting a need to a solution isn't as easy as it sounds, but failing to do so honestly ultimately ends in disaster.

If you find yourself persuading your client he or she really needs what you're selling, you've already lost the sale. Remember, while your customer may not always completely understand his or her needs, they will always understand their circumstance and situation better than you. When you convince yourself that you have a better handle on the situation than the customer, you are setting yourself up for a world of hurt. The key to avoiding this is simple: listen.

True listening isn't about waiting to talk or thinking of ways to counter the person's objection while they are still voicing their objection. It's about trying to understand the need. It is disappointing to go on a sales call only to learn that the prospect doesn't need what you're selling. In those circumstances, help them find a solution even if you don't sell it. I do this and even though I don't benefit immediately, I tend to be the first person called when the customer needs something again.

3. Don't sell people what they need, sell them what they want.

One of my favorite lines from a television show comes from The Rockford Files. For those of you who never watched the James Garner antihero private detective show, stop reading this and go watch at least three episodes. Go on, this article will be here when you get back.

Now, for those of you familiar with the show, you probably remember Angel Martin, who was Jim Rockford's ex-con, all-purpose, low-life buddy. Always on the grift, Angel once said, "Nobody ever made a thin dime selling people what they need; you gotta sell them what they want."

Now, assuming you are not a grifter, the trick is to get people to want what they need. This is neither as easy nor as hard as it sounds. Ever bought a roof? It's easy to admit that you need a roof. It takes one talented salesperson to get you to want to buy a roof, but if you don't get them to want to buy a roof they will simply go to the cheapest provider. The key is to get the customer comfortable with you (as distinct from your company) because you are the person who can reduce their stress. You can make promises and make sure that they are kept. You have a name and a face. You can ultimately be held accountable for the claims you have made.

4. People buy from people they like.

A friend of mine used to rep art for a major advertising agency that catered to high-end, sophisticated clients. He started in the matting room putting the cardboard frames around the works of art. Occasionally, he was asked to fill in for the driver delivering art to the client. My friend could not contain his excitement when the client was opening the package. Talking a mile a minute, he would sputter out "wait until you see this next one ....check out the detail here ...look at the colors there." He was practically jumping out of his skin with excitement.

Pretty soon, customers were asking for him to deliver the art, which quickly morphed into him selling the art to the customers. He was remarkably good at it. (He is an incredibly talented artist in his own right and has since left sales to work for a major video game developer drawing guns, soldiers and buildings.) People wanted to buy from my friend because he was genuinely excited about the art work. His enthusiasm was contagious. Creative directors who looked at one drawing after another with not much discernible difference were drawn to art this crazy rep was genuinely giddy about it. You can't fake that. You can't expect anybody to get all that excited unless you are selling something you would be genuinely excited to buy.